Sympatric Ant Species Research Articles

From hybridization to introgression between two closely related sympatric ant species

From hybridization to introgression between two closely related sympatric ant species

Genetic and chemical divergence among host races of a socially parasitic ant.

Host–parasite associations facilitate the action of reciprocal selection and can drive rapid evolutionary change. When multiple host species are available to a single parasite, parallel specialization on different hosts may promote the action of diversifying natural selection and divergence via host race formation. Here, we examine a population of the kidnapper ant (Polyergus mexicanus) that is an obligate social parasite of three sympatric ant species: Formica accreta, F. argentea, and F. subaenescens (formerly F. fusca). Behavioral and ecological observations of P. mexicanus have shown that individual colonies parasitize only one species of host and that new Polyergus queens maintain host fidelity when establishing new colonies. To successfully adapt to a particular host, Polyergus ants may mimic or camouflage themselves with the species‐specific chemical cues (cuticular hydrocarbons) that their hosts use to ascertain colony membership. To investigate the extent of host specialization, we collected both genetic and chemical data from P. mexicanus that parasitize each of the three different Formica species in sympatry. We show that host‐associated genetic structure exists for both maternally inherited mitochondrial DNA data and biparentally inherited microsatellite markers. We also show that P. mexicanus can be distinguished by chemical profile according to host due to partial matching with their host. Our results support the hypothesis that host race formation is occurring among lineages of P. mexicanus that use different Formica hosts. Thus, this system may represent a promising model for illuminating the early steps of divergence, accumulation of reproductive isolation, and speciation.

Interspecific variation in neighbour–stranger discrimination in ants of theNeoponera apicaliscomplex

1. The ecological success of social insects lies in their ability to prevent the exploitation of colony resources by competitors or parasites. Nestmate recognition is therefore of crucial importance in maintaining the integrity of the colony. Furthermore, inter‐colony competitive relationships are often complex, as many species discriminate between neighbours and strangers, with reduced (the dear enemy phenomenon) or increased levels of aggression towards nearby colonies, depending on the species. In this context, between‐species comparisons could be particularly helpful to investigate the proximate causes underlying this context‐dependent phenomenon, but these are notoriously lacking.2. Here an attempt was made to circumvent this drawback by studying three closely related sympatric ant species with very similar life histories that belong to theNeoponera apicaliscomplex. The present study investigated how nestmate recognition and inter‐colony competitive relationships were influenced by spatial, chemical and genetic distances between colonies.3. It was found that one species,N. apicalismorph 7, showed a clear dear enemy phenomenon with no influence of chemical and genetic distances, suggesting the existence of a learning process. In contrast,N. apicalismorph 4 andNeoponera verenaemorph 1 failed to show any strong discrimination between close and distant non‐nestmates.4. These results are discussed in the light of the observed interspecific variation in nesting preferences, possibly constraining the opportunities of familiarisation between nearby nests, and modulating the competition for resources between colonies.5. It is argued that this study further reinforces the relative threat level hypothesis as an ultimate explanation for neighbour–stranger discrimination processes.

Reactions by army ant workers to nestmates having had contact with sympatric ant species

It was recently shown that Pheidole megacephala colonies (an invasive species originating from Africa) counterattack when raided by the army ant, Eciton burchellii. The subsequent contact permits Pheidole cuticular compounds (that constitute the “colony odour”) to be transferred onto the raiding Eciton, which are then not recognised by their colony-mates and killed. Using a simple method for transferring cuticular compounds, we tested if this phenomenon occurs for Neotropical ants. Eciton workers rubbed with ants from four sympatric species were released among their colony-mates. Individuals rubbed with Solenopsis saevissima or Camponotus blandus workers were attacked, but not those rubbed with Atta sexdens, Pheidole fallax or with colony-mates (control lot). So, the chemicals of certain sympatric ant species, but not others, trigger intra-colonial aggressiveness in Eciton. We conclude that prey-ant chemicals might have played a role in the evolution of army ant predatory behaviour, likely influencing prey specialization in certain cases.

Eye structure, activity rhythms, and visually-driven behavior are tuned to visual niche in ants.

Insects have evolved physiological adaptations and behavioral strategies that allow them to cope with a broad spectrum of environmental challenges and contribute to their evolutionary success. Visual performance plays a key role in this success. Correlates between life style and eye organization have been reported in various insect species. Yet, if and how visual ecology translates effectively into different visual discrimination and learning capabilities has been less explored. Here we report results from optical and behavioral analyses performed in two sympatric ant species, Formica cunicularia and Camponotus aethiops. We show that the former are diurnal while the latter are cathemeral. Accordingly, F. cunicularia workers present compound eyes with higher resolution, while C. aethiops workers exhibit eyes with lower resolution but higher sensitivity. The discrimination and learning of visual stimuli differs significantly between these species in controlled dual-choice experiments: discrimination learning of small-field visual stimuli is achieved by F. cunicularia but not by C. aethiops, while both species master the discrimination of large-field visual stimuli. Our work thus provides a paradigmatic example about how timing of foraging activities and visual environment match the organization of compound eyes and visually-driven behavior. This correspondence underlines the relevance of an ecological/evolutionary framework for analyses in behavioral neuroscience.

Polygyny in the nest-site limited acacia-ant Crematogaster mimosae

Polygyny is common in social insects despite inevitable decreases in nestmate relatedness and reductions to the inclusive fitness returns for cooperating non-reproductive individuals. We studied the prevalence and mode of polygyny in the African acacia-ant Crematogaster mimosae. These ants compete intensively with neighboring colonies of conspecifics and with three sympatric ant species for resources associated with the whistling-thorn acacias in which they all obligately nest. We used the genotypes of alate males at ten microsatellite loci to reconstruct queen genotypes and found that C. mimosae colonies are frequently secondarily polygynous, in that they include multiple closely related (and sometimes full-sib) queens, and (more rarely) unrelated queens. We also found that individual queens in both monogynous and polygynous colonies had mated with multiple males, making C. mimosae an interesting example of simultaneous polygyny and polyandry. The presence of polygyny in C. mimosae and the intense competition for nest-sites between C. mimosae and its conspecifics support the association between nest-site limitation and polygyny. Polygyny may allow for increased worker populations and a competitive advantage, as inter-colony conflicts are typically won by the colony with the larger number of workers.

Nest distribution varies with dispersal method and familiarity-mediated aggression for two sympatric ants

Dispersal mechanisms and competition together play a key role in the spatial distribution of a population. Species that disperse via fission are likely to experience high levels of localized competitive pressure from conspecifics relative to species that disperse in other ways. Although fission dispersal occurs in many species, its ecological and behavioural effects remain unclear. We compared foraging effort, nest spatial distribution and aggression of two sympatric ant species that differ in reproductive dispersal: Streblognathus peetersi, which disperse by group fission, and Plectroctena mandibularis, which disperse by solitary wingless queens. We found that although both species share space and have similar foraging strategies, they differ in nest distribution and aggressive behaviour. The spatial distribution of S. peetersi nests was extremely aggregated, and workers were less aggressive towards conspecifics from nearby nests than towards distant conspecifics and all heterospecific workers. By contrast, the spatial distribution of P. mandibularis nests was overdispersed, and workers were equally aggressive towards conspecific and heterospecific competitors regardless of nest distance. Finally, laboratory experiments showed that familiarity led to the positive relationship between aggression and nest distance in S. peetersi. While unfamiliar individuals were initially aggressive, the level of aggression decreased within 1 h of contact, and continued to decrease over 24 h. Furthermore, individuals from near nests that were not aggressive could be induced to aggression after prolonged isolation. Overall, these results suggest that low aggression mediated by familiarity could provide benefits for a species with fission reproduction and an aggregated spatial distribution.

Interactions Between Aphaenogaster carolinensis (Hymenoptera: Formicidae) and Four Sympatric Ant Species

Individual ants of Aphaenogaster carolinensis Wheeler were placed in two way combinations with four sympatric ant species (Aphaenogaster lamellidens Mayr, Crematogaster lineolata Say, Pachycondyla chinensis Emery and Prenolepis imparis Say) to determine whether their interspecific behavior was dependent upon the ant species they were confronted with. The tendency of A. carolinensis to initiate and terminate interactions, and the durations of those interactions, were measured for all combinations. There was no significant effect of species on initiation or termination. There was a significant effect of species on the duration of interactions that were both initiated and terminated by A. carolinensis. Durations of interactions with A. lamellidens were significantly longer than with other species. The conclusion is that the interspecific behavior of A. carolinensis is dependent in part on the species it is interacting with.

Inter- and Intraspecific Aggression in the Invasive Longlegged Ant (Hymenoptera: Formicidae)

The longlegged ant, Anoplolepis gracilipes (Fr. Smith) (Hymenoptera: Formicidae), is a highly invasive species that can aggressively displace other ant species. We conducted laboratory assays to examine interspecies aggression of A. gracilipes versus 15 sympatric ant species found in the urban environment and disturbed habitat in Malaysia: Monomorium pharaonis (L.), Monomorium floricola (Jerdon), Monomorium orientale Mayr, Monomorium destructor (Jerdon), Pheidole parva Mayr, Crematogaster sp., Solenopsis geminata (F.), Tapinoma indicum (Forel), Tapinoma melanocephalum (F.), Technomyrmnex butteli Forel, Dolichoderus thoracicus (Smith), Paratrechina longicornis (Latrielle), Oecophylla smaragdina (F), Camponotus sp., and Tetraponera rufonigra (Jerdon). A. gracilipes showed aggressive behavior toward all opponent species, except the smallest M. orientale. Opponent species size (body size, head width, and mandible width) was significantly correlated with A. gracilipes aggression level and mortality rate. We also found a significant positive relationship between A. gracilipes aggression level and the mortality of the opponent species. The results suggest that invasive populations of A. gracilipes would have the greatest impact on larger ant species. In addition, we examined the intraspecific aggression of A. gracilipes. We found that A. gracilipes from different localities in Malaysia showed intraspecific aggression toward one another. This finding differs from the results of studies conducted in Christmas Island earlier. Differences in the genetic variability among populations may explain these differing results.

Foraging behaviors of two sympatric ant species in response to lizard eggs

The trade-off between behavioral dominance and resource discovery ability represents a mechanism which could facilitate the coexistence of species, but evidence of the existence of this trade-off is limited and is often derived from experiments using artificial bait. In this study, I performed a field experiment to investigate the outcome of potential food competition between an encounter species ( Paratrechina longicornis) and an exploitative one ( Pheidole taivanensis) and to examine the factors that may explain the behavior of P. taivanensis when obtaining food (lizard eggs) without being attacked by P. longicornis. When P. longicornis was experimentally introduced to eggs occupied by P. taivanensis for 1 day, it displaced P. taivanensis. However, P. longicornis ignored lizard eggs which had been occupied by P. taivanensis for 2 or more days, and did not displace P. taivanensis, because by that time the eggshells had been damaged by P. taivanensis so they could no longer be used by P. longicornis. Eggshells were damaged more quickly by P. taivanensis at Santimen, southwestern Taiwan, than at four other study sites where there were lower intensities of food competition between P. taivanensis and P. longicornis. The displacement percentage was higher at Santimen which had higher ant population densities. The present study shows that lizard eggs may constitute a natural, ephemeral resource for which ants compete in space and time. Comparisons between study sites with and without ants suggest the existence of a trade-off between resource discovery and territorial defense.

Territorial aggressiveness on the arboreal ant Azteca alfari by Camponotus blandus in French Guiana due to behavioural constraints

This study reports new information on interactions between two sympatric ant species, the plant-ant Azteca alfari (Dolichoderinae) living in association with the myrmecophyte Cecropia obtusa (Cecropiaceae) and Camponotus blandus (Formicinae), a ground-nesting, arboreal-foraging species. Workers of A. alfari forage only on the foliage and the upper parts of the trunk of their host Cecropia, while C. blandus nests in the ground but frequently forages and patrols pioneer tree foliage, including Cecropia. The activity pattern of A. alfari and the number of C. blandus on Cecropia obtusa was monitored hourly during a two-day period in a disturbed area in French Guiana. The maximum activity of C. blandus occurred between 8:30 and 12:30, at which time A. alfari had retreated within the domatia and were least present on the trunks. Even though aggressive confrontations were observed, C. blandus workers often initiate confrontations but do not prey on A. alfari nor exploit food bodies produced by Cecropia, the principal food source of A. alfari. Hence hostility appears to be the result of territoriality. Differences in their foraging rhythms are proposed as promoting resource and territory partitioning in this ant assemblage. To cite this article: M. McClure et al., C. R. Biologies 331 (2008).

Specialized predation on Wasmannia auropunctata by the army ant species Neivamyrmex compressinodis

Abstract: We report here the first case of an efficient and specialized predator of the invasive ant species Wasmannia auropunctata: the army ant Neivamyrmex compressinodis. Our results are based on a study that we conducted in French Guiana, a part of the Wasmannia’s native range. When N. compressinodis workers attacked W. auropunctata nests, the assaulted workers panicked and left the nests, some of them carrying brood. Nevertheless, during its raids on W. auropunctata, N. compressinodis was able to capture nearly all of the W. auropunctata brood and winged sexuals, whereas none of the attacks by N. compressinodis on other sympatric ant species were successful. Laboratory experiments revealed that the workers of eight compared sympatric species attacked the N. compressinodis individuals and that N. compressinodis workers accepted W. auropunctata brood as well as that of most of the tested species, showing that its specificity probably depends on the reaction of the W. auropunctata workers.

Complex display behaviour during the intraspecific interactions of myrmecomorphic jumping spiders (Araneae, Salticidae)

Jumping spiders (Salticidae) are known for their elaborate vision‐based display behaviour, and a sizeable minority of the species in this large family resemble ants. The display repertoire of two ant‐like salticid species from the Philippines is investigated. Myrmarachne assimilis is a specialist ant mimic, closely matching the appearance of the weaver ant Oecophylla smaragdina. Myrmarachne bakeri is a generalist mimic, which, although ant‐like, is not a close match to any sympatric ant species. Myrmarachne are sexually dimorphic, with males having enlarged chelicerae. The copulatory posture of Myrmarachne is unique among salticids, apparently as an adjustment for the male's elongated chelicerae. Details concerning the intraspecific behaviour of Myrmarachne appear to be adjustments to living in environments populated by numerous other animals with similar appearance (ants). However, the specialist and the generalist that were investigated have display repertoires that are broadly similar to each other and to those of more typical salticids. Generally, the display behaviour of Myrmarachne appears not to have necessitated dramatic deviation from typical salticid display and mating strategies.

Extensive exchange of fungal cultivars between sympatric species of fungus-growing ants.

Fungal cultivars of fungus-growing ants (Attini, Formicidae) are carried by dispersing queens from parent to offspring nest. This vertical cultivar transmission between generations is thought to result in long-term ant-fungus coevolution and selection for beneficial cultivar traits that maximize harvests and thus colony productivity. In contrast to this traditional view of vertical cultivar transmission, frequent horizontal cultivar transmission between ant species is implicated by a phylogenetic analysis of 72 cultivars propagated by two fungus-growing ant species coexisting sympatrically in central Panama. The two ant species are specialized on the same group of closely related cultivars, but in six of 12 cultivar clades identifiable within this group, cultivars from both ant species were united in the same clade. Five of these 'mixed' clades were supported by bootstrap values of about 90% or higher. In one instance, colonies from the two ant species cultivated the same, genetically identical, cultivar clone. These phylogenetic patterns indicate that: (i) cultivar exchanges between the two ant species occur routinely throughout ecological time; and that (ii) coevolutionary processes between ants and their fungi are more diffuse than previously assumed. Because the two ant species are specialized on a narrow group of closely related cultivars that they regularly exchange among each other, but not with other sympatric ant species, cultivar exchanges are constrained, most likely, by ant preferences for their own cultivar group or by stringent selection against transitions of ant lineages to distantly related cultivars.

Exploitation of an ant chemical alarm signal by the zodariid spiderHabronestes bradleyiWalckenaer

Intraspecific signals are vulnerable to exploitation by predators that are not the targets of the signal. This cost has been documented for several acoustic, visual and chemical signals, but not for chemical alarm pheromones. We reveal a novel form of exploitation of an ant alarm pheromone by the cursorial spider Habronestes bradleyi (Zodariidae), a specialist predator of the highly territorial and aggressive meat ant Iridomyrmex purpureus. We demonstrate experimentally that H. bradleyi locates I. purpureus workers engaged in territorial interactions with conspecifics, by using the alarm pheromone of the ants as a cue. The spiders are attracted to an airborne cue, identified as the alarm pheromone 6-methyl-5-hepten-2-one, which is produced by injured or alarmed I. purpureus workers but not by inactive I. purpureus, or injured workers of other sympatric ant species. These data demonstrate a novel cost of producing alarm pheromones.

Maximization of foraging efficiency and resource defense by group retrieval in the ant Formica schaufussi

Workers of the ant Formica schaufussi forage as individuals and cooperate in groups to retrieve arthropod prey. In 2 sample years, group-transported prey were on average 6.8 and 4.7 times heavier than individually retrieved items, and the average loading ratios of groups were greater than the loading ratios of single foragers. Retrieval group size was adjusted to prey size, and prey transport velocity for individuals and groups tended to decrease with increasing prey weight. The efficiency of individual and group retrieval, estimated from calculations of the prey delivery rate to the nest (PDR) achieved by each foraging mode, varied as a function of prey size. Individual retrieval maximized PDR at a prey weight of 19.5 mg, and group transport maximized PDR at 190 mg. Although the PDR maxima of an individual in a group and a solitary forager were approximately equal, depending on prey size, group transport may maximize foraging efficiency. Group transport also decreased interference competition from sympatric ant species. Group-transported prey having a greater likelihood of successful retrieval were within the size range of prey that maximized foraging efficiency. Transport group size appeared to be more important in prey defense than in increasing prey transport velocity, suggesting an important role of group size in competitive ability.

Etude de la récolte de nourriture par la fourmi polymorphePheidole pallidula dans son milieu naturel

The dimorphic ant specicsP. pallidula is widespread in all Mediterranean countries and was the dominant species in our study area. Demographic data such as relative abundance, density, spatial distribution were collected and quantitative observations ofP. pallidula behaviour were made at the time of food exploitation. This allowed us to discern the relations, particularly competitives ones, between their workers and other sympatric ant species (Aphaenogaster senilis, Crematogaster sordidula, Messor barbara, Plagiolepis pygmaea). The ecological success ofP. pallidula seems to depend on 3 main characteristics of its ethology: 1o) its foraging activity both diurnal and nocturnal, 2o) the diversity of its foraging techniques (individual and collective retrievals by minor foragers; short and long lasting foraging trails). 3o) the active participation of majors in intense exploitation of large unretrievable food sources where they could be very efficient to protect food sources from competitors and/or to cut preys' sclcrites. These majors are mainly present on food sources and on trails, exploration of the foraging area being ensured by the minor caste. The adaptive significance of caste polyethism ofP. pallidula species during food exploitation is discussed according to our field data.

Chemical interference competition by Monomorium minimum (Hymenoptera: Formicidae).

Workers of Monomorium minimum forage above-ground for dead arthropods. Small particles (<1 mg) are retrieved individually, but larger particles stimulate recruitment and are dissected by groups of workers. The recruitment pheromone originates in the Dufour's gland and the number of ants responding to a trail varies with pheromone concentration. When ants of other species are encountered at food resources, workers of M. minimum gaster-flag and extrude an irritating poison gland secretion from the sting. This chemical interference delays invasion by competitors and prolongs the period during which the colony can dissect and retrieve pieces of the food resource. M. minimum recruits at higher temperatures than sympatric ant species. The probability of interference at food baits rises from 5% to 100% when they become too large for a single worker to carry. The probability of food resource loss is higher for baits of intermediate weight (x=18.1 mg) than for those of low weight (x=0.1 mg) or high weight (x=403.1 mg).